Currently, the transportation, storage and use of oil involve procedures including pipeline delivery, transportation of railway oil tank car and automobile oil tank car, tanker transportation, oil depot storage, gas station storage, etc. Since the floating-roof technology is adopted in the oil depot storage, over 90% breathing loss of oil is reduced. However, large and small tank breathing still happens in other procedures, resulting in evaporation loss and quality degradation of oil as well as environmental pollution. Also, large and small tank breathing may even lead to a high risk of fire and explosion.
The breathing loss shall in the following be further described with gasoline as an example.
According to Gasoline and Oil Gas Emission Control Standard for Oil Product Sales Industry by the Safety and Environmental Protection Bureau of China Sinopec Group Corporation, gasoline suffers around 1% loss during such procedures as railway oil tank and automobile oil tank transportation, oil tanker storage, gas station storage; annual consumption of gasoline in China is over 50 million tons, with a loss of more than 500,000 tons. As oil price exceeds 7000 yuan/ton at present, the cost amounts to more than 3.5 billion yuan, excluding the loss of apparatus (automobile) oil tank.
Also, oil vapor pollutes environment. With most gas stations situated around urban areas, each certain unit of oil vapor is able to pollute air of 2000 times the volume of said oil vapor. Generally, during the process of transportation and sales, 50 million tons of gasoline will produce oil vapor of at least 5 times the volume of the gasoline, amounting to 340 million cubic meters. This means that 680 billion cubic meters of air will be polluted. Since oil vapor reacts with toxic gas in the air under the radiation of ultraviolet ray, more toxic pollutants will be produced and do more harm to human body as well as destroy the ozone layer (the oil vapor recycling reform in Beijing has been completed before the 2008 Olympic Games). Moreover, oil vapor increases the possibility of fire and explosion which is more destructive to ecological environment.
Through large and small tank breathing, the water vapor in the air enters the storage tank and becomes liquid water when interior temperature decreases, which then adversely affects the quality of oil products.
Besides gasoline, there are many other highly volatile products such as solvent oil, naphtha, aviation kerosene, light diesel oil, crude oil, etc. The evaporation of these oil products result in greater loss and more severe environmental pollution.
Although some tank cars, gas stations and storage depots may recycle the oil vapor through adsorption, condensation and absorption or membrane separation, the recycling needs large investment, consumes energy resources and is not efficient. A set of recycling equipment for a storage depot is as expensive as 5˜15 million yuan and one for a gas station 0.3˜1 million yuan. According to the operation of installed equipment in Taiwan and the Mainland China, the recycling equipment has a high failure rate and a high maintenance fee; most of the recycled oil vapor is of no use but to be burnt. Moreover, oil vapor, mixed with air, can be of greater danger during transportation. Therefore, the fundamental and most efficient way to solve the problem is to deal with at the very beginning of the generation of oil vapor.